6 J. H. SMITH, Bleach-out Process of Colour Photography. 



which adjoins it, but they are capable of passing through 

 a layer of lesser affinity in order to reach a medium of 

 greater affinity, and that whether the layer of lesser 

 affinity contained already a dye of its own affinity or not 



Absolutely neutral media probably do not exist, and 

 it was not found practicable to separate dyes in media of 

 low affinity from media of high affinity by means of in- 

 sulating layers. 



As former workers had used both acid and basic dyes 

 it was quite natural that they had met with the difficulty 

 of getting them to remain in one and the same vehicle, 

 and that Szczepanik had sought to overcome the difficulty 

 by separating the dyes into different layers. We had been 

 successful in finding a series of basic dyes which had no 

 tendency to migrate from their emulsion, collodion, as 

 long as this was separated from the body of the paper 

 support (for which the basic dyes have a similar, although 

 mostly inferior, affinity to collodion) by a layer of gelatine. 



This first paper which I manufactured under the name 

 of " Uto " paper was used chiefly for the reproduction of 

 coloured window transparencies, "Glacier" prints, natural 

 leaves and flowers, three-colour transparencies and the 

 like. 



In the summer of 1907 the Autochrome plate was put 

 on the market by Lumiere Bros, in Lyons, and it was 

 hoped that the " Uto " paper would be found adapted for 

 the reproduction of these plates. Unfortunately this was 

 found not to be the case. Many difficulties had still to be 

 overcome and improvements had to be made before this 

 result could be accomplished, and I was engaged upon 

 this investigation during the following four years. 



It was found necessary to obtain : — 



(a) The annihilation of the reproduction of the 

 Autochrome colour screen. 



